Stomach 1 + 2 Flashcards
What are the functions of the stomach?
Stores food
Starts digestion of protein
Innate defence (acidic)
Little bit of car and fat digestion
What is the term given to the digested food leaving the stomach entering into the duodenum?
Is it acidic or alkaline?
Chyme
Acidic
What are the 3 general parts of the stomach?
Fundus
Body
Antrum
What is the name of the point where the oesophageal tissue becomes stomach tissue? (The first part of the stomach the oesophagus leads into?)
Cardia
How does the type of cell change as it goes from the oesophageal tissue to the stomach tissue (cardia)?
Lower oesophagus = stratified squamous
Stomach/cardia = simple columnar
What are the 2 sphincters helping controlling the movement of contents through the stomach?
Lower oesophageal sphincter
Pyloric sphincter
What are sphincters made out of?
Smooth muscle rings
What is the function of the lower oesophageal sphincter?
Prevent reflux of stomach contents to oesophagus
What is the function of the pyloric sphincter?
Controls release of chyme into the duodenum from the stomach
What aids the lower oesophageal sphincter to remain closed?
Right crus of the diaphragm wraps around it
Acute angle
What part of the stomach is the Fundus?
What part of the stomach is the body?
What part of the stomach is the antrum?
Fundus = upper 1/3
Body = middle 1/3
Antrum = lower 1/3
Go to the last slide of Stomach 1 and label the stomach:
1 = pyloric sphincter
2 = antrum
3 = body
4 = Fundus
5 = right crus of diaphragm
6 = lower oesophageal sphincter
What is the function of the Rugae in the stomach?
They are numerous folds in the walls of the stomach which can allow the stomach to expand
What is receptive relaxation?
The peristalsis of food through the oesophagus towards the stomach leads to the reflex relexation of the proximal stomach (Fundus distends) so stomach can fill without a significant rise in pressure
What are the 3 layers of muscle in the stomach from innermost to outwards?
Oblique
Circular
Longitudinal
How does the thickeners of the muscle wall change as you move from proximal to distal?
Thinner proximal
Thicker more muscular distal
What is the significance of the thickness of the muscular walls of the stomach getting thicker as you go from proximal to distal?
Food moves faster as it descends
Meaning smaller parts can advance on but larger bits of food remain to be further digested
What cells line the entire surface of the stomach?
Surface mucus cells
What is the importance of surface mucus cells lining the entire surface of the stomach?
Produce a protective layer of mucus to protect underlying epithelia
What are gastric pits?
Invaginations of the epithelium of the stomach
What do the gastric pits lead to in the stomach?
Gastric glands
What cells are found in the gastric glands?
Parietal cells
Chief cells
Enteroendocrine cells (like G cells)
What is the function of parietal cells?
Produce stomach acid
What is the function of chief cells?
Release pepsinogen = inactive form of pepsin (is a protease)
Where are the majority of parietal cells located?
Body of stomach
Where are the majority of G cells located?
What are there function?
Antrum
Produce Gastrin
What are some protective mechanisms of the stomach?
Produce bicarbonate on the epithelial membrane to help keep layer neutral
Stomach cells regularly replaced
Prostaglandins made to support mucosal blood flow which supports the protective mucus layer
What is the important pump that gets put on the apical membrane of a parietal cell when it needs to produce stomach acid?
Proton pump = H+/K+ ATPase
What are the 2 states a parietal cell can be in?
Resting state
Active state
What is a parietal cell like in the resting state?
Normal apical membrane
Proton pumps contained within tubulovesicles within the parietal cell
What happens to a parietal cell when it becomes activated?
Apical membrane invaginates forming canaliculi+microvilli to make its SA large
Tubulovesicles fuse with canaliculi so proton pumps can pump into the stomach lumen
What are the 3 phases of digestion?
Cephalic phase
Gastric phase
Intestinal phase
What are some sensory triggers that lead to the cephalic phase of digestion/acid production?
Smell
Sight
Taste
What are some gastric triggers that lead to the production of acid?
gastric phase of digestion
Stretch
Presence of amino acids and small peptides
Food acts as a buffer higher pH
What are some intestinal triggers leading to the production of HCl?
Chyme in duodenum/ presence of partially digested proteins
What are the 3 receptors that can be activated to stimulate a parietal cell?
Gastrin receptors
Histamine receptors
Muscarinic receptors
What simulates G cells to produce Gastrin?
Peptides in stomach lumen
What type of receptors does Gastrin bind to on a parietal cell?
Cholecystokinin receptors
How is acid production stimulated by vagal stimulation?
ACh can bind to receptors on the G cell leading to Gastrin production
ACh can bind directly to Muscarinic receptors directly on the parietal cell
How does Histamine stimulate acid production?
Entero-chromaffin like cell (ECL) makes histamine which binds to H2 receptors on Parietal cell making it produce HCl
ECL also has a Muscarinic ACh receptor
What cell inhibits acid production in the stomach?
D cell
What hormone do D cells produce to inhibit acid production?
Somatostatin
When do D cells secrete somatostatin?
When the pH in the stomach is very low (too acidic)
What is the brief process of HCl being produced by the parietal cells?
Water + CO2 makes carbonic acid
Carbonic acid dissociates to H+ and HCO3- (carbonic acid catalyses)
H+ pumped out into stomach lumen across H+/K+ ATPase (apical membrane)
Bicarbonate ions pumped into venous blood antiport with Cl-
What is the alkaline tide?
The venous blood leaving the stomach is more alkaline due to the anions antiporter on the basal membrane exchanging HCO3- with Cl- in the parietal cell
What substances stimulate parietal cells to produce stomach acid?
Gastrin (CCK receptors)
ACh (Muscarinic receptors)
Histamine (H2 receptors)
Look at last slide of Stomach 2, label the parietal cell
1 = H2O
2 = CO2
3 = carbonic anhydrase
4 = H+
5 = H+/K+ ATPase
6 = Cl-
